OS information missing in SPDX format SBOM for a container image

**What happened**:

When generating an SPDX for container images like Redis or Ubuntu, only package information is included, but OS information, such as Alpine or Ubuntu, is not included in the [Package Information section](https://spdx.github.io/spdx-spec/v2.3/package-information/).

Redis:
https://gist.github.com/kl-sinclair/eec66cc2a577a4c702521b20217a1bac

Ubuntu:
https://gist.github.com/kl-sinclair/dfab9b10e93be204d8d76b69e2662333

**What you expected to happen**:

OS information should be included as a package. For example, as follows:

```json
...
"packages": [
...
{
"name": "alpine",
"SPDXID": "SPDXRef-OperatingSystem-alpine-xxxxxxxxxxxxxxxx",
"versionInfo": "3.20.1",
"downloadLocation": "NONE",
"filesAnalyzed": false,
...
"primaryPackagePurpose": "OPERATING-SYSTEM"
}
...
```

or

```tag-value
##### Package: ubuntu

PackageName: ubuntu
SPDXID: SPDXRef-OperatingSystem-ubuntu-xxxxxxxxxxxxxxxx
PackageVersion: 24.04
PackageDownloadLocation: NONE
PrimaryPackagePurpose: OPERATING-SYSTEM
FilesAnalyzed: false
...
```

**Steps to reproduce the issue**:

```sh
syft scan redis:6-alpine -o spdx-json=syft-redis.spdx.json
syft scan ubuntu:latest -o spdx-json=syft-ubuntu.spdx.json
```

**Anything else we need to know?**:

With CycloneDX, OS information is included as a component:

[syft-redis.cdx.json](https://gist.github.com/kl-sinclair/4e21d77760b539304241b8550d3bec01):

```json
...
"components": [
...
{
"bom-ref": "os:alpine@3.16.0",
"type": "operating-system",
"name": "alpine",
"version": "3.16.0",
"description": "Alpine Linux v3.16",
"swid": {
"tagId": "alpine",
"name": "alpine",
"version": "3.16.0"
},
"externalReferences": [
{
"url": "https://gitlab.alpinelinux.org/alpine/aports/-/issues",
"type": "issue-tracker"
},
{
"url": "https://alpinelinux.org/",
"type": "website"
}
],
"properties": [
{
"name": "syft:distro:id",
"value": "alpine"
},
{
"name": "syft:distro:prettyName",
"value": "Alpine Linux v3.16"
},
{
"name": "syft:distro:versionID",
"value": "3.16.0"
}
]
}
...
```

[syft-ubuntu.cdx.json](https://gist.github.com/kl-sinclair/ccd042d97b1c1c8c7974a573a87013fb):

```json
...
"components": [
...
{
"bom-ref": "os:ubuntu@22.04",
"type": "operating-system",
"name": "ubuntu",
"version": "22.04",
"description": "Ubuntu 22.04.1 LTS",
"swid": {
"tagId": "ubuntu",
"name": "ubuntu",
"version": "22.04"
},
"externalReferences": [
{
"url": "https://bugs.launchpad.net/ubuntu/",
"type": "issue-tracker"
},
{
"url": "https://www.ubuntu.com/",
"type": "website"
},
{
"url": "https://help.ubuntu.com/",
"comment": "support",
"type": "other"
},
{
"url": "https://www.ubuntu.com/legal/terms-and-policies/privacy-policy",
"comment": "privacyPolicy",
"type": "other"
}
],
"properties": [
{
"name": "syft:distro:id",
"value": "ubuntu"
},
{
"name": "syft:distro:idLike:0",
"value": "debian"
},
{
"name": "syft:distro:prettyName",
"value": "Ubuntu 22.04.1 LTS"
},
{
"name": "syft:distro:versionCodename",
"value": "jammy"
},
{
"name": "syft:distro:versionID",
"value": "22.04"
}
]
}
...
```

**Environment**:
- Output of `syft version`:

```sh
$ syft version
Application: syft
Version: 1.8.0
BuildDate: 2024-06-24T15:27:29Z
GitCommit: Homebrew
GitDescription: [not provided]
Platform: darwin/amd64
GoVersion: go1.22.4
Compiler: gc
```

- OS (e.g: `cat /etc/os-release` or similar):
macOS Ventura 13.3

Start by reproducing the issue with `syft scan redis:6-alpine -o spdx-json=...` and `syft scan ubuntu:latest -o spdx-json=...`, then trace the SPDX output path and compare it with the CycloneDX result shown in the issue. Done means the detected operating system appears as an SPDX package with its name, version, and `OPERATING-SYSTEM` purpose in both JSON and tag-value output.

Written by the indexing model from the issue text.